A single-lens reflex camera is known, in which a single lens is used as both an image-capturing lens and a finder lens so that incident light from the image-capturing lens is reflected by a mirror to allow it to be seen in a finder. The single-lens reflex camera allows a photographer to change the lens so as to take photos in accordance with the scenes where photos are taken and in accordance with the needs of the photographer. The light incident upon the finder's optical system is obtained by reflecting the light incident from the lens using the mirror, and when a photo is taken, the mirror is retracted, and the light incident from the lens reaches the film as it is. Accordingly, when the single-lens reflex camera is used, there is an advantage in that it is possible to take a picture of a subject which is seen in the finder exactly as the shown image without any parallax.
In order to provide a single-lens reflex camera with an autofocus sensor, a single-lens reflex camera is known, in which a mirror is made of a semi-transparent mirror, and transmission light is passed to an autofocus sensor using a still another sub-mirror (for example, see Patent Documents 1 and 2). In such single-lens reflex cameras, autofocus (hereinafter, autofocus is referred to as AF as necessary) is performed until the shutter is triggered.
As described above, the single-lens reflex camera changes the position of the movable mirror, thereby switching which of the finder's optical system and the film the incident light is passed to. This means that, at the instance at which a subject is photographed (exposed), it is impossible to see the subject through the finder. When the semi-transparent mirror and the sub-mirror is provided in the configuration, it is necessary to retract both of the semi-transparent mirror and the sub-mirror to a retraction position, and this makes it difficult to cause the AF to function normally when continuous shooting is performed.
Accordingly, a configuration to abolish the sub-mirror and make the semi-transparent mirror as a fixed-type has been suggested (for example, see Patent Document 3). In the configuration as disclosed in Patent Document 3, reflection light from the semi-transparent mirror is passed on to the AF sensor unit, and transmission light therefrom is passed on to the image-capturing device. According to the configuration as disclosed in Patent Document 3, a subject can be seen at all times even during exposure, and the AF can be performed at all times.
However, when the semi-transparent mirror is made as the fixed-type, multiple reflection occurs within the semi-transparent mirror, and an image that does not actually exist (hereinafter referred to as a ghost as necessary) may appear. This kind of phenomenon also occurs when an infrared (IR) cut filter and an ultraviolet (UV) cut filter are provided on one surface of the semi-transparent mirror.
In particular, in a digital camera, it is easy to enlarge a taken digital image, and the ghost is likely to cause problems.